Loud-speaker diaphragm and mounting



June 2, 1953 J, B, BRENNAN 2,640,556

LOUD-SPEAKER DIAPHRAGM AND MOUNTING Filed July 25, 1947 *lumin Y A A ""gl, y 3/ (111,@ 3]

:lY/;'//////// /6 /7 22 Z3 Patented June 2, 1953 UNITED STATES PATENT OFFICE LOUD-SPEAKER DIAPHRAGM AND MOUNTING Joseph B. Brennan, Cleveland, rOhio Applicationv July 25, 1947, Serial No. 763,718

7 Claims. 1

This invention relates to loud-speaker constructions and particularly to the formation of spiders and diaphragms for loud-speakers.

Heretofore speaker diaphragms have generally been formed either by splitting sheets, rolling them into a cone and cementing them or by depositing bers from a wet suspension onto a suitable form. Spiders` are generally formed from sheet material such as impregnated cloth or accreted wet pulp suspensions or paper.

I have found that both diaphragme and spiders can be formed advantageously by a dry method as more particularly described and claimed for example, in my copending application Serial No. 695,806', filed September 9, 1946. In this method fibers of the desired material are mixed with particles of a dry thermo-plastic binder and are heated and pressed to produce the necessary density and to bind the fibers together.

The present application relates to the fermation of speaker members by a dry method and is applicable to the formation of both diaphragme and spiders. One of its objects is to provide speaker members having high strength and which can be of substantially any desired rigidity and porosity.

Another object is to provide a loudspeaker con-- struction in which the diaphragm or the spider or both are formed .by crossedy layers of fibers joined at. spaced points by binding material.

Still another object is to provide a loudspeaker in which carded layers or sheets of fibers mixedwith bers or particles of dry binding material are stacked with the iibers in adjacent layers crossed andare pressed and treated to cause the binding material to join the fibers. The binding material may be in the form ofr granules or of strands and is preferably thermo-plastic so that the treatment thereof may consist in pressing atr an elevated temperature.

l A further object is to provide a spider for a loud-speaker which serves also as a lter.

In practicing the invention any desired fibers or mixtures of fibers which are relatively heat resistant can be used, such as kapok, cotton, jute, fiber wool or synthetic fibers. For diaphragms, light soft fibersy such as lrapok or cotton are preferred while for spiders metal or synthetic fibers mixed with cotton or kapok may be preferred to provide increased rigidity. By heat resistant fibers is meant those materials, either natural or synthetic, which are unaffected at the temperatures required to soften and set the thermo-plastic material described hereinafter.

The liber is mixed with a dry binding material which is preferably a thermo-plastic material.

Suitable materials for this purpose include cellulose acetate, nylon, vinyl resins or other synthetic resins or mixtures thereof. Any material which will adhere to the bers when heated and which retains its flexibility and is stable at normal temperatures or when set is satisfactory. The binding material may be used in the form. of relatively small granules but is preferably formed into strands or filaments of approximately the same diameter as the fibers.

The bers and binding material are mixed in the desired proportions and are carded to form loose layers or sheets in which the fibers lie generally parallel. The amount of binding material used may vary depending on the stiffness and porosity desired but is preferably insufficient to ll the spaces between the nbers, even when compressed, so that the -bers will be joined only at spaced points to leave spaces through which air can pass. This is particularly important in the formation of spiders although in diaphragms a greater percentage of binding material can be used to ll completely or almost completely the spaces between the fibers. In, for instance, the body of diaphragms an extra layer of thermoplastic fibers may be incorporated.

After the carded layers or sheets are formed, they are stacked with the fibers in adjacent sheets crossing each other. The bers may cross at right angles or at some other desired angle pare ticularly when a relatively large number of sheets are used. The stacked sheets are then subjected to heat and pressure to compress the material to the desired extent and to soften the binder so that it will join the fibers. The sheets may be pressed in a mold to produce the desired final shape directly or may lbe pressed into fiat sheets which are subsequentlytrimmed and molded to shape.

In the pressing and heating operation the thermo-plastic binder will soften and will adhere to the adjacent heat resistant fibers. Because generally insufficient binder is used to nil all of the spaces between the bers they will be joined only at spaced points by spaced discrete masses of binder which may be sufficient to produce the desired degree of stiffness. At the same time the material will be compressed to the desired density.

In making diaphragme either suicient binder may be used to ll the spaces between the bers to produce an impervious sheet or preferably the sheet may be dipped in or sprayed with a ller such as lacquer to make it impervious. Variations in the stiffness of the diaphragm in diiferent areas may be produced by cutting the layers or sheets to the necessary shape and building them up to greater thickness in the areas where increased stiffness is desired. Also some variation in stiffness can be produced by spotting the lacquer coating on the completed and pressed material.

In making spiders the layers or sheets of carded fibers with thermo-plastic binder mixed therewith can be pressed to the desired shape utilizing a suicient thickness of fiber layers to produce the necessary stiffness. In this case the structure is left porous so that air can pass freely through it to permit breathing of the diaphragm. At the same time because the fibers lie relatively close together the spider will act as a filter to keep foreign materials away from the air gap and specifically away from the voice coil. By building the fiber layers up to the proper thickness and by using the proper proportion of thermo-plastic binder any desired stiffness in the spider can be produced.

One speaker construction embodying the present invention is illustrated by way of example in the accompanying drawings in which- Figure 1 is an axial section through a speaker embodying the invention;

Figure 2 is a partial section showing an alternative spider construction;

Figure 3 is a diagram illustrating a step in the formation of a diagram; and

Figure 4 is an enlarged partial section illustrating the manner in which the fibers are connected in the nal construction.

As shown in Figure l, the speaker includes a generally conical diaphragm I having a reduced neck Il at its center to which a voice f coil supporting member may be connected or integrally formed and terminating at its large end in a supporting flange I2. The diaphragm body is connected to the flange l2 by a connecting portion formed with annular corrugations I3 displaced from each other parallel to the axis of the diaphragm. The diaphragm may be constructed as described in detail above to provide a relatively flexible impervious structure capable of free vibration under the influence of the voice coil.

The diaphragm is mounted in a housing which may be constructed as of metal and which is formed with a generally conical or cylindrical side wall portion I4 terminating at one end in a ange I5 to which the mounting flange I2 of the diaphragm may be secured.

The housing includes a magnetic pole piece I6 provided with a central opening to receive the core I1 of a field coil I8. may be supported from the pole piece by means of a bracket I9 to maintain the pole piece in centered position. The field coil is enclosed in a housing 2| secured to the speaker housing I4.

The diaphragm is driven by means of a voice coil 22 lying between the field coil core I1 and the pole piece I6 and carried by a tubular extension 23 secured to the flange I I of the speaker.

The speaker and voice coil are held centered by a spider which is formed with an edge flange 24 by means of which it is rigidly mounted on the pole piece IB. 'Io the flange is integrally joined a cylindrical upwardly extending wall portion 25 which terminates in an upper flexible body portion 26. The body portion is preferably formed with a series of annular corrugations to increase its flexibility and has a central opening to fit over the neck II or the voice coil support 23 to hold the voice coil centered. The spider may be integrally formed of crossed The field coil p 4 sheets or layers of carded material in the same manner as the diaphragm and as explained more fully above.

According to one feature of the invention the diaphragm may be made of any desired flexibility to produce any desired resonance and is preferably of varying thickness in different portions thereof to produce a varying stiffness. For example, as shown in Figure l, the conical body portion I0 of the diaphragm may be relatively thick while the edge portion including the corrugations I3 may be made thinner to increase the flexibility. According to the present method this can be accomplished by employing carded sheets or laminations of different sizes which are so stacked as to produce the desired variations in thickness.

In addition the resonance may further be varied by varying such factors as the amount of thermoplastic binder employed and the pressure, time and temperature of the bonding operation. It will be understood that a larger proportion of thermo plastic bonding material and higher pressure and temperature tend to increase the density of the diaphragm material to control its resonance. Combinations of these several manners of producing variations in flexibility are preferably employed such for example as by utilizing more carded layers in certain areas of the diaphragm by varying the proportion of thermo-plastic binder employed in different portions of the diaphragm and by varying the pressure and perhaps the temperature in different areas of the diaphragm during the molding or pressing operation. I have also found that subsequent waterproofing requirements such as by lacquering are greatly reduced or eliminated in certain types of diaphragms manufactured in accordance with the present invention.

In the diaphragm, as shown in Figure 1, a dust cap or web is preferably provided closing the central opening in the diaphragm through the neck Il as indicated at 21. This web may be formed integral with the diaphragm of carded material similar to the diaphragm itself and may be bonded to the diaphragm to form an integral structure during the molding operation. Preferably the web is bowed upward as shown to stiffen the central neck portion of the diaphragm and may be made impervious or porous, as desired.

Figure 2 illustrates an alternative construction in which the parts identical with corresponding parts in Figure l are indicated by the same reference numerals. In this construction the diaphragm as shown at 28 terminates in an annular open neck 29 at its small end. The spider is formed with an edge mounting flange 3| and a central continuous body portion 32 connected to the edge flange by annular corrugations 33 displaced from each other in a direction at right angles to the plane of the mounting flange. Adjacent its center the body portion is formed with an annular groove into which the neck 29 of the diaphragm may fit and may be secured to the central part of the spider body portion forming the dust cap or web for the diaphragm.

In the constructions as so far described in which several individual parts such as the speaker diaphragm, the spider and perhaps the coil support 23 are formed of fibers and thermoplastic binder as described above, such components may be bonded together by a hot pressing operation. If desired,..all'of the partscould' be placed in a single mold andpressed simultaneouslyto produce an integrallyv bonded `structure therebyy eliminatingr the necessityA for cement-and insuring tight and permanent, connection-of the parts. Where it is not feasible to placealli of thepartsin a mold, they; may be separately molded andmay be joined by subjecting the overlapping portions thereof to heat and pressure. This isnot only a less expensi-veoperatioxr.than cementing but produces a more satislactory speaker construction.

One step in the' methodl of' forming a diaphragmxis shown by illustration in Figure 3'. This ligure'y illustrates tlfi'efmanner` of forming a diaphragm of the type shown in Figure l in which the web or dust cap is integral with the diaphragm and illustrates the manner of obtaining portions of diiierent thickness. As shown, one or more sheets or laminations 34 of carded material mixed with strands or particles of thermoplastic binder may be provided which are of a size to extend completely to the edge of the mounting flange I2. These sheets or laminations may be stacked with one or more sheets or laminations 35 of smaller size suilicient to extend only to the edge of the speaker body portion I0. A central neck portion 36 formed of loose carded fibers may be centrally located with respect to the laminations 3d and 35 and the entire stack may then be subjected to heat and pressure in a mold. It is possible according to the present invention first to mold blanks which may be relatively iiat or partially shaped in the first molding operation and subsequently to completely form the diaphragm in a later operation.

Alternatively, developed out out blanks of crossed layers of carded fiber having thermoplastic binding material mixed therein may be formed into the desired shape and simultaneously bonded in a heated mold to make diaphragms or spiders without the use of cement. The crossing of the layers may be accomplished by crossing small cut out sections of carded sheets or layers or by crossing the carded sheets or layers and then severing the desired sections. The cutting out may be accomplished before or after or simultaneously with the pressing of the superimposed or stacked layers as may best meet the production requirements. It is generally desirable, however, to use cut out sections of different sizes or shapes to make one diaphragm or spider. In this Way, for instance, the edge area of a diaphragm may be made thinner and more flexible than the body portion.

Figure 4 illustrates in detail a portion of the construction of a diaphragm or spider formed according to the present invention. As shown, the structure is formed of a plurality of elongated bers 31 of a heat resistant material such as those enumerated above. The fibers are arranged in layers with the bers in each layer being carded so that they are generally parallel and the libers in adjacent layers cross each other, as shown. The fibers may cross at any desired angle, although for most purposes it is preferred to cross them at approximately a right angle, as shown. The iibers are held together by spaced particles 38 of thermo-plastic binding material so that free lengths of fibers exist between the particles. The spacing between the particles of binding material is determined by the proportion of thermo-plastic binder employed so that the stiffness and porosity are also affected by the degree of compression employed in the molding1 and4 by: thecharacterv ofi v they fibrous material` employed. In any casevwhere a fil-ler is not used the completed ystructureA willi be porous andthefibers will -be'y spacedl relatively closely so that they will function,aszaffllterxl While the invention `has been described in detail in connection with the particular methods and loud-speaker constructions, itwillbe Vunderstood that these are illustrative only and are not to be taken as adeflnitionl of` the yscope of the invention, reference beingfhadY for this purpose tothe :appended claims..`

Whatis claimed is:

l. In. a loud-speaker construction,`v af thin ywalled-ffvibratile member comprising azplura'lity of layers of fibers with the bers in each layer generally parallel to each other and the fibers in adjacent layers crossing each other, and spaced masses of binding material joining the fibers at points at which they touch each other.

2. In a loud-speaker construction, a spider for a vibratile diaphragm comprising a thin walled cupped body formed by a plurality of layers of ibers with the fibers in each layer generally parallel and the iibers in adjacent layers crossing each other, and discrete masses of binding material joining the bers at spaced points, said body being porous and the iibers lying close enough together to form an effective iilter.

3. In a loud-speaker construction, a spider for a vibratile diaphragm comprising a thin Walled cupped body having a generally cylindrical Wall portion formed at `one end with a peripheral flange for mounting the spider on a support and having an integral flexible Wall at its opposite end formed with a series of annular corrugations, said body being formed of a plurality of layers of fibers with the iibers in each layer lying generally parallel and with the fibers in adjacent layers crossing each other, and separate masses of binding material joining the fibers at spaced points.

4. In a loud-speaker construction, a vibratile diaphragm comprising a thin-walled generally conical member formed of a plurality of layers of bers with the fibers in each layer generally parallel and the fibers in adjacent layers crossing each other, separate masses of binding material joining the fibers at spaced points, and a coating over at least one surface of the member making it impervious to air.

5. A vibratile member for loud-speakers comprising a plurality of laminations of generally parallel heat resistant bers with the bers in adjacent laminations crossing each other, and discrete particles of thermo-plastic material bonding together the laminations and the iibers within the laminations, the laminations being of different sizes to provide portions of diiierent thickness in the member.

6. A vibratile diaphragm for loud-speakers comprising a dished body portion and a flexible integral edge flange portion, the diaphragm being formed of a plurality of laminations of generally parallel heat resistant bers with the fibers in adjacent laminations crossing each other, and discrete particles of thermo-plastic material bonding together the laminations and the iibers Within the laminations, certain of the laminations extending over the entire diaphragm and other laminations extending over the dished body portion only.

7. In a loud speaker construction, a vibratile diaphragm comprising a thin-walled generally conical member formed of a plurality of layers of bers with the fibers in each layer generally parallel to each other and the fibers in adjacent layers crossing each other, and spaced masses of binding material joining the bers at points at which they touch each other.

JOSEPH B. BRENNAN.

References Cited in the le of this patent UNITED STATES PATENTS Number Number Name Date Metcalf July 20, 1937 Brennan Aug. 17, 1937 Nagelvoort Feb. 14, 1939 Stephan May 14, 1940 Maxwell Dec. 14, 1943 Francis, Jr. Sept. 5, 1944 Koon Mar. 27, 1945 Brennan Sept. 24, 1946 Francis, Jr. Jan. 25, 1949 Olson Dec. 6, 1949 FOREIGN PATENTS Country Date Great Britain Mar. 13, 1939 

